Vessel hulls have traditionally been optimized for use in either shallow water or in deep water. For example, to navigate shallow waters, a relatively flat hull is used to maximize displacement and minimize draft. On the other hand, vessels that operate in deep waters frequently have v-shaped hulls that provide deep draft for good seakeeping.
If a vessel is designed for use in shallow waters, its performance in deep waters will be compromised, and vice-versa. This has spurred the development of variable-draft vessels, which are designed to operate well in both shallow and deep waters.
As the name implies, a variable-draft vessel is capable of varying its draft to accommodate changes in water depth or mission requirements. A variable-draft vessel that is disclosed in U.S. Pat. No. 6,877,450 B2 is capable of reconfiguring its hull form to change draft. The vessel includes a flat, center hull that is coupled to two side hulls. The center hull is vertically movable relative to the side hulls to vary draft.
According to the patent, the center hull can be moved above or below the waterline. When the center hull is above the waterline, all buoyancy is provided by the side hulls, and the vessel takes maximum draft. As the center hull dips below the waterline, it contributes to the buoyancy provided by the side hulls. As a consequence, vessel draft is reduced.
While variable-draft vessels are an advance over traditional fixed draft designs, they do have certain drawbacks. For example, the variable-draft vessels with a movable center hull that are disclosed in U.S. Pat. No. 6,877,450 B2 are not capable of varying draft independently of the center hull, unless buoyancy is altered through the use of ballast tanks, etc. This limits the extent to which this type of variable-draft vessel can be reconfigured.